Glass ceramic compositions of interest to this invention include those disclosed in, for example, Japanese Patent Application Laid-Open No. 2002-29827 (Patent Document 1) and Japanese Patent Application Laid-Open No. 2003-63861 (Patent Document 2).
First, Patent Document 1 discloses a composite laminate ceramic electronic component obtained by stacking high-dielectric-constant ceramic layers with a relatively high relative permittivity and low-dielectric-constant ceramic layers with a relatively low relative permittivity, and in particular, as a glass ceramic composition for forming the low-dielectric-constant ceramic layers, discloses, in claim 1 thereof, a glass ceramic composition containing a MgAl2O4-based ceramic and glass. More particularly, a glass ceramic composition which contains: a MgAl2O4-based ceramic powder; and a glass powder containing 13 to 50 weight % of silicon oxide in terms of SiO2, 8 to 60 weight % of boron oxide in terms of B2O3, 0 to 20 weight % of aluminum oxide in terms of Al2O3, and 10 to 55 weight % of magnesium oxide in terms of MgO is disclosed.
In addition, Patent Document 1 discloses, in claim 2 thereof, an alkaline-earth metal oxide which may be further contained in a proportion of 20 weight % or less, and in claim 6 thereof, the glass content which may preferably be 20 to 80 weight % of the total.
The glass ceramic composition disclosed in Patent Document 1 achieves, in the case of a sintered body thereof, a relatively low relative permittivity such as, for example, 8 or less, and can be thus made suitable for high-frequency applications.
Next, Patent Document 2 discloses a composite laminate ceramic electronic component obtained by stacking high-dielectric-constant ceramic layers with a relatively high relative permittivity and low-dielectric-constant ceramic layers with a relatively low relative permittivity.
In particular, the high-dielectric-constant material constituting the high-dielectric-constant layer includes BaO—TiO2—RE2O3 (RE is a rare-earth element) based dielectric and glass. The glass contains, according to claim 2 of Patent Document 2, 10 to 25 weight % of SiO2, 10 to 40 weight % of B2O2, 25 to 55 weight % of MgO, 0 to 20 weight % of ZnO, 0 to 15 weight % of Al2O2, 0.5 to 10 weight % of Li2O, and 0 to 10 weight % of RO(R is at least one of Ba, Sr, and Ca). In addition, as disclosed in claim 4 of Patent Document 2, the content of the glass is preferably 15 to 35 weight %.
On the other hand, Patent Document 2 discloses a material similar to that in Patent Document 1, as a low-dielectric-constant material constituting the low-dielectric-constant ceramic layers.
The inventors of the present application have first found insulation reliability to be further improved, as a result of making further experiments on the respective glass ceramic compositions described in Patent Documents 1 and 2 mentioned above. The cause is assumed as follows.
The glass contained in the glass ceramic composition disclosed in each of Patent Documents 1 and 2 is intended to allow firing at a temperature of 1000° C. or lower, and adjusted in terms of composition to be likely to be crystallized. In the case of the glass ceramic compositions described in Patent Documents 1 and 2, the glass component and the ceramic component react to deposit crystals in the firing process, and it is thus difficult to stabilize the crystal quantity and the quantity of the glass component at the time of firing completed. Further, this instability of the crystal quantity and the quantity of the glass component at the time of firing completed is assumed to decrease the insulation reliability.
For example, the glass contained in the glass ceramic compositions described in each of Patent Documents 1 and 2 contains a relatively large amount of MgO, this large amount of MgO in the glass is believed to deposit crystals of MgAl2O4 and/or Mg2SiO4 from the glass component, and this deposition is assumed to lead to a decrease in insulation reliability.
In addition, in particular, the high-dielectric-constant material described in Patent Document 2 requires the addition of glass in order to allow firing at temperatures of 1000° C. or less, and on the other hand, requires a BaO—TiO2—RE2O3 based dielectric contained in order to increase the relative permittivity. However, free Ti ions from the BaO—TiO2—RE2O2 based dielectric cause oxygen defects. Furthermore, these oxygen defects can cause a decrease in insulation reliability in use at high temperature and high voltage for a long period of time, etc.
In addition, the inventors of the present application have recognized, as a result of repeated experiments, problems of the compositions of the respective glass ceramic compositions described in Patent Documents 1 and 2, such as difficulty in stably achieving desired relative permittivity in a wide range from low relative permittivity to high relative permittivity.
More specifically, the glass contained in the glass ceramic compositions described in Patent Documents 1 and 2 is likely to react with the ceramic component to be crystallized in the firing process as described previously. When the crystals are deposited, the relative permittivity is changed, and it is thus difficult to achieve desired relative permittivity.
In addition, the glass contained in the glass ceramic compositions described in Patent Documents 1 and 2 fails to have favorable wettability to MgAl2O4 based ceramics or BaO—TiO2—RE2O2 based dielectrics. Therefore, the glass ceramic composition is not able to be sintered, unless a relatively large amount of glass is added. However, the large additive amount of glass will decrease the relative permittivity. Thus, it is difficult to prepare, in particular, high-dielectric-constant materials.    Patent Document 1: Japanese Patent Application Laid-Open No. 2002-29827    Patent Document 2: Japanese Patent Application Laid-Open No. 2003-63861